1. Field of the Invention
The present invention relates to a curtain airbag that is inflated and deployed along a side face section inside a vehicle cabin for the purpose of vehicle occupant protection during a lateral collision or rollover (overturning) of a vehicle.
2. Related Technology
In recent years, high levels of safety performance have been required of vehicles. This trend is shared across countries around the world, where most vehicles are currently standard-equipped with airbags as vehicle safety devices. Firms involved in vehicle development have adopted ongoing safety improvements as a major development guideline. In keeping with this, new airbags are continually being developed.
Standards for evaluating vehicle safety differ from country to country, and firms approach product development such that products can meet evaluation standards in multiple countries. In the United States, for instance, which has the largest automobile fleet in the world, Federal Motor Vehicle Safety Standards (FMVSS) are issued by the National Highway Traffic Safety Administration (NHTSA). At present, in a Notice of Proposed Rulemaking (NPRM, Docket Number: NHTSA-2009-0183) for FMVSS, scheduled to be issued by the NHTSA, a requirement is proposed that aims at “reducing the probability of occupant ejection from a vehicle through a side window using an ejection mitigation system in the event of a side impact crash or rollover (overturning)”. The requirement can be met by providing a curtain airbag as a device intended to reduce ejection from a vehicle, such that the curtain airbag constitutes the ejection mitigation system.
A curtain airbag is an airbag disposed above a door and that inflates and deploys along vehicle side windows, upon occurrence of an impact, to protect an occupant thereby (for instance, Japanese Patent Application Publication No. 2006-111199. An ordinary curtain airbag is designed to have a pressure duration, when inflated and deployed, longer than that of a front airbag or the like. That is because the time during which an impact unfolds is lengthened if, for instance, rollover follows the lateral collision. Thus, the curtain airbag is intended to maintain the inflated state until and during rollover, to restrain thereby the occupant, and prevent the occupant from being ejected from the vehicle.
At present, yet better ejection mitigation performance is required of airbags. The inflation region of ordinary curtain airbags is partitioned into a plurality of divisions (chambers). The chamber against which the occupant strikes, from among the plurality of chambers, differs depending on the circumstances at the time of impact. During rollover, for instance, it is observed that the posture of the occupant of the front seat collapses significantly, and the head of the occupant is likely to strike the front chamber at the frontmost side of the vehicle. Unlike a chamber around the middle, which is connected, on both sides to other chambers in the front-rear direction of the vehicle, the front chamber is connected only to another chamber from the rear. Therefore, the load received by the front chamber was hardly absorbed by other chambers, and the displacement amount of the front chamber towards the vehicle exterior was larger than that of other chambers.